Detonators are used to detonate a main charge such as an explosive of an air to surface missile. Such detonators are also used to detonate explosives used in other tactical devices, construction explosives, rocket boosters, and the like. These types of detonators must be physically robust and of high integrity. For example, an air to surface missile may be designed to pierce a bunker or other building and only then detonate the primary explosive. The detonator must, therefore, survive the shock of the launch and the impact with the bunker.
Exploding foil initiator ("EFI") detonators, (e.g. "chip slappers"), generally include a ceramic chip upon which is deposited two opposing conductive copper lands which taper to a narrow "bridge" portion therebetween. An electrical current is provided to the lands at the time of initiation and the bridge portion bursts sending a flying plate thereon into an explosive charge which, in turn, detonates the main charge.
It is convenient to package the chip and the explosive charge within a standard electronics housing such as a "TO" type transistor package including a base with one or more electrical leads and a can which covers the base. Such detonator packaging techniques, however, are fraught with problems.
First, one important design consideration is that the explosive charge must contact the inside top surface of the transistor package can in order to prevent energy losses.
Due to loose manufacturing tolerances, however, the length of the transistor can, the height of the header wall of the transistor base, the thickness of the explosive charge, and the thickness of the chip can all vary. To accommodate these variations and to ensure that the explosive charge is in intimate contact with the inside of the can, the prior art methods included forcing the total height of the components inside the can (e.g., the chip, the spacer, and the explosive charge) to always be greater than the length of the transistor can through the use of a resilient member or members disposed inside the can below the explosive charge. The resilient member is compressed by exerting pressure on the can and the rim of the can is then welded to the flange of the base.
One problem with this prior art design is the complexity involved in choosing the structure and orientation of the resilient member which often includes incorporating two explosive charges separated by the resilient member. And, these additional components add to the cost of the detonators and the man hours required for their fabrication.
Second, the lead posts of the transistor package base are typically connected to the lands of the chip slapper by individual wires. These wires tend to break in the harsh environment described above and/or burn under the application of high amperage current. In addition, securing the individual wires to the lands and lead posts involves a considerable amount of man hours.
One attempt at overcoming the breakage and burning problems includes interconnecting a number of individual wires from each lead to the lands thereby providing redundancy should any one wire break or burn. This solution, however, only adds to the complexity of the design and entails additional man hours required to interconnect each additional wire.
Another problem with present chip slapper detonator designs is that once the wires are in place, some kind of a mechanical spacer element must be placed between the EFI and the explosive charge to optimize the spacing therebetween thereby assuring that the flying plate travels the correct distance before striking the explosive charge. These mechanical spacer elements must be carefully designed and selected--often involving additional man hours in the fabrication of the detonators resulting in higher costs.